Cutting structure for single roller cone drill bit

ABSTRACT

A roller cone drill bit is disclosed which includes a bit body adapted to be coupled to a drill string. A bearing journal depends from the bit body. A single roller cone is rotatably attached to the bearing journal. The roller cone is formed from steel and includes a plurality of cutting elements disposed at selected positions about the cone. At least one of the cutting elements has an extending body which has a first end coupled to the roller cone and a distal end extending away from the cone. The extending body is formed from steel. A super hard element is coupled to the distal end of the extending body to form a super hard cutting face for the cutting element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 60/538,745 filed on Jan. 23, 2004,titled “Cutting Structure for Single Roller Cone Drill Bit,” which isnow incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of roller cone (“rock”)bits used to drill wellbores through earth formations. Morespecifically, the invention is related to the structure of cuttingelements used in roller cone bits having a single roller cone.

2. Background Art

Roller cone drill bits are commonly used in the oil and gas industry todrill well bores through earth formations. One example of a conventionaldrilling system used to drill a well bore is shown in FIG. 1. Thedrilling system includes a drilling rig 10 used to turn a drill string12 which extends downward into a wellbore 14. Connected to the end ofthe drill string 12 is a roller cone drill bit 20.

The most common type of roller cone bit is a three cone bit (illustratedat 20 in FIG. 1). A three cone bit 20 includes a bit body adapted to becoupled to a drilling tool assembly or “drill string” which rotates thebit as it is pressed axially into the formations being drilled. The bitbody includes three legs, each having a bearing journal thereon. Agenerally conical roller cone is rotatably mounted to each bearingjournal. During drilling, the roller cones are pressed against aformation and rotate about the respective journals while the bit isrotated under an axial load on the formation. A plurality of cuttingelements is disposed on each of the roller cones, typically in rows. Thecutting elements extend from the surface of the cones to engage andbreak up formation as the bit is rotated.

One particular type of roller cone drill bit is a single cone bit, whichincludes only one leg, one bearing journal and one roller cone rotatablymounted on the bearing journal. The drill diameter of the single rollercone bit is substantially concentric with an axis of rotation of thedrill bit. This type of drill bit has been shown to be particularlyuseful in drilling small diameter wellbores (e.g., less than about 4 to6 inches [10 to 15 cm]) because the bearing structure can be largerrelative to the diameter of the drilled hole when the bit has only oneconcentric roller. This is in contrast to the typical three cone bit, inwhich each journal must be smaller relative to the drilled holediameter. Having a significantly larger radial bearing for the same bitdiameter than a comparable three roller cone bit allows for higher loadsto be placed on the single cone bit to increase the rate of penetrationof the drill bit.

One of the limitations of single cone roller bits is that the cuttingelements tend to experience greater wear over time due to shearingaction, compared to cutting elements on a two or three cone bits. Thecutting elements on the single cone bit undergo as much as an order ofmagnitude more shear than do the cutting elements on a conventional twoor three cone bit. Large amounts of shear on cutting elements of singlecone bits become apparent when looking at the bottomhole patterns ofeach type of bit. Single roller cone bits typically drill out a “bowl”shaped bottomhole geometry. The cutting elements on the single cone bitgenerally shear the formation creating multiple grooves laid out inhemispherically projected hypotrochoids. In contrast, a two or threecone bit generates a series of individual craters or indentations duringdrilling. Shearing rock typically causes more wear on a cutting elementthan impacting the rock to compressively fail it. The cutting elementson single cone bits also go through large changes in their direction ofmotion during drilling, typically anywhere from 100 to 360 degrees. Suchchanges require special consideration in design.

The single roller cone drill bit efficiently drills the portion of thewellbore proximate the center of the bottom hole because a large portionof the cutting structure near the center of the hole remains in movingcontact with the formation during drilling. However, as a result, thewear of the cutting elements on a single cone bit is typically notuniform. In general, cutting elements in the zone that cuts the bottomof a borehole being drilled typically maintain substantially constantcontact with the formation during drilling, and cutting elements in thezone that primarily contacts the side wall of the bore hole have moreintermittent contact with the formation. Therefore, the cutting elementsnear the bottom are worn more quickly. As cutting elements are worn andbecame dull, the cutting efficiency of the bit significantly declinesand the effective life of the bit is unduly limited. This is furtherdiscussed in U.S. Pat. No. 6,119,797 entitled “Single Cone Earth BoringBit”, which is incorporated herein by reference.

Cutting element wear in the zone that primarily contacts the side wallis also an important consideration in bit design because an essentialperformance aspect of any drill bit is its ability to drill a wellborehaving the full nominal diameter of the drill bit from the time the bitis first used to the time it becomes worn and must be replaced. In thecase of a single roller cone bit, several of the cutting elements on thesingle roller cone eventually engage the wellbore wall at the gagediameter. As the cutting structure wears, the drilled diameter of thewellbore may be substantially reduced. The reduction in wellborediameter can be an intolerable condition and may require reaming withsubsequent bits or the use of reamers or other devices designed toenlarge the wellbore diameter. Moreover, the reduced wellbore diameterwill decrease the flow area available for the proper circulation ofdrilling fluids and bit cuttings. The use of bits, reamers, or otherdevices to ream the wellbore can incur substantial cost if the bottomhole assembly must be tripped in and out of the hole several times tocomplete the procedure.

Drill bit life and efficiency are of great importance because the rateof penetration (ROP) of the bit through earth formations is related tothe wear condition of the bit. Accordingly, various methods have beenused to provide abrasion protection for drill bits in general, andspecifically for roller cones and cutting elements. For example, rollercones, cutting elements, and other bit surfaces have been coated withhardfacing material to provide more abrasion resistant surfaces.Further, specialized cutting element insert materials have beendeveloped to optimize longevity of the cutting elements. While thesemethods of protection have met with some success, wear is still aproblem for single cone bits.

To address the problems of wear associated with single cone bits,diamond enhanced inserts consisting of a polycrystalline diamond layerbonded to a tungsten carbide/cobalt substrate in a HTHP process havebeen proposed and used as cutting elements for single cone bits.Examples of diamond enhanced inserts and other super hard inserts arefurther described in U.S. Pat. Nos. 4,525,178, 4,606,106, 4,797,241,4,650,776, 5,271,749, 5,326,380 and incorporated herein by reference.Such inserts have been used on the nose portion of a cone as a “bearingsurface” or on the entire cone as cutting elements. Due to theprohibitive cost of large diamond enhanced inserts, inserts used onsingle cone bits have been generally small with very limited extensionsfrom the cone surface. The short extension of diamond enhanced insertslimits penetration of the formation and cuttings removal duringdrilling. Thus, while bit life has been improved, the rate ofpenetration of these bits has been unduly limited. To over come thislimitation, larger diamond enhanced inserts with longer extensions aredesired, but the high cost and fragility associated with these largerdiamond enhanced inserts have shown them to be unsuitable and unfeasiblefor commercial products.

A cutting element structure for a single cone roller bit that provideswear resistance without sacrificing toughness and/or cutter extension isdesired.

SUMMARY OF INVENTION

In one aspect, the present invention relates to single roller cone drillbit. The drill bit includes a single rotatable cone formed from steeland having at least one cutting element disposed at a selected positionthereon. The at least one cutting element includes an extending bodyformed from steel which has a first end coupled to the cone and a distalend extending away from the cone. A super hard element is coupled to thedistal end of the extending body to form at least a portion of a cuttingsurface for the cutting element.

In another aspect, the invention relates to a method for making a drillbit. The method includes rotationally coupling a roller cone to ajournal of a single roller cone drill bit body, and providing at aselected position on the cone a cutting element comprising an extendingbody formed from steel and a super hard element coupled to a distal endof the extending body to form at least a part of an outer surface of theinsert.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows one example of a conventional drilling system.

FIG. 2 shows a generalized cut away view of a single roller cone drillbit.

FIG. 3 shows a cone of a single cone drill bit having a cuttingstructure in accordance with one embodiment of the present invention.

FIG. 4 shows a single cone drill bit having a cutting structure inaccordance with another embodiment of the present invention.

FIG. 5 shows an enlarged cross-section view of a cutting element inaccordance with one embodiment of the present invention shown in FIG. 4.

FIG. 5A shows another example of a super hard element in accordance withan embodiment of the present invention.

FIG. 6 shows another example of a single cone bit in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

A general structure for a single cone roller cone drill bit which can bemade according to various embodiments of the invention is shown in a cutaway view in FIG. 2. The bit 22 includes a body 23 made of steel orother high strength material. The body 23 includes a coupling 24 at oneend adapted to join the bit body 23 to a drill string (not shown) forrotating the bit 22 during drilling. The bit body 23 may also includegage protection pads 25 at circumferentially spaced apart positionsabout the bit body 23. The gage protection pads 25 may include gageprotection inserts 26 in some embodiments. The gage protection pads 25if used, extend to a drill diameter 27 of the bit 22.

Another end of the bit body 23 includes a bearing journal 23A to which asingle roller cone 28 is rotatably mounted. In some embodiments, thecone 28 may be locked onto the journal 23A by locking balls 23B disposedin the corresponding grooves on the outer surface of the journal 23A andthe interior surface of the cone 28. The means by which the cone 28 isrotatably locked onto the journal 23A is not meant to limit the scope ofthe invention. The cone 28 is formed from steel or other high strengthmaterial and may be covered about its exterior surface with hardfacingor similar material intended to reduce abrasive wear of the cone 28. Insome embodiments, the cone 28 will include a seal 29 disposed to excludefluid and debris from entering the space between the inside of the cone28 and the journal 23A. Such seals are well known in the art.

The cone 28 includes a plurality of cutting elements 31, 32 thereon atselected positions. The journal 23A depends from the bit body 23 suchthat it defines an angle α between the rotational axis 33 of the journal23A and the rotational axis 34 of the bit 22. The size of this angle αwill depend on features such as the nature of the earth formation beingdrilled by the bit. Nonetheless, because the bit body 23 and the cone 28rotate about different axes, the motion of the cutting elements 31, 32during drilling can be roughly defined as falling within a wallcontacting zone 35, in which cutting elements 32 located therein atleast intermittently contact the outer diameter (wall) of the wellbore,and a bottom contacting zone 36, in which cutting elements 31 locatedtherein are in substantially continuous contact with the earthformations, and generally do not contact the outer diameter (wall) ofthe wellbore during drilling.

The cutting elements 32 in the wall contacting zone 35 define the drilldiameter of the bit. Having cutting elements for the wall contactingzone 35 which provide good toughness, minimize axial wear, and maintainsuitable cutting action against formation being drilled, can extend thelife of the bit, while helping to provide relatively high rates ofpenetration. The cutting elements 31 in the bottom contacting zone 36significantly effect on the rate of penetration through formations.Having cutting elements in the bottom contacting zone 36 which minimizeaxial wear and provide adequate strength and toughness that allows forincrease cutting element extension to aggressively cut throughformations, can also extend the life of the bit and provide forincreased rates of penetration. Issues related to single roller conedrill bits are further described in U.S. application Ser. No.10/407,922, titled “Single Cone Rock Bit Having Inserts Adapted toMaintain Hole Gage During Drilling” and U.S. patent application Ser. No.10/498,822, titled “Cutting Element Structure for Single Roller ConeBit,” which are both assigned to the assignee of the present inventionand incorporated herein by reference.

In accordance with one aspect of the present invention, FIG. 3 shows anexample cutting structure for a single cone bit. The roller cone 42 ofthe bit is formed from steel and includes a plurality of cuttingelements 43 formed on the outer surface of the cone at selectedpositions. The cutting elements 43 are generally arranged in rows. Atleast one of the cutting elements 43 (cutting element 44) comprises amilled steel tooth having a steel extending body 45 formed on the outersurface of the cone 42. The extending body 45 extends outward from thesurface of the cone 42 with an axial length (primary extension length),b. The cutting element 44 further includes a super hard element 46 pressfit into a socket (not shown separately) formed at a distal end of theextending body 45. The super hard element 46 is positioned to extendfrom a surface of the extending body 45 by a distance (secondaryextension length), t, such that it engages with and cuts through earthformations during drilling. The super hard element 46 is exposed at thedistal end of the extending body 45 to provide a super hard and wearresistant cutting face for the cutting element 44.

Also, as shown in FIG. 3, in one or more embodiments of the inventionthe extending body 45 may be configured to extend substantially from thecone surface to form an aggressive cutting structure for the bit. Thedistal end of the extending body 45 may truncate to a substantiallyplanar surface. The exposed surface of the super hard element 46 whichforms the cutting face of the cutting element 44 may have a convex shapewith a truncated, substantially planar tip. The other cutting elements43 on the cone 42 may have a configuration similar to that of cuttingelement 44.

The cutting structure shown in FIG. 3 is just one example of a cuttingstructure for a single cone bit in accordance with the presentinvention. In other embodiments, the cutting elements may compriseinserts instead of teeth and may have different configurations dependingon their position on the cone. The super hard material may be disposedat different selected positions proximal the distal end of the cuttingelement. Also, in other embodiments, different types of cutting elementsmay be included at selected locations on the cone. The cutting elementsmay have different abrasion resistances, such as higher near the nose ofthe cone than near the gage, to provide for more even wear of thecutting elements during drilling. Having cutting elements comprising anextending body formed from steel with a super hard cutting face,advantageously, provides greater impact toughness than a fully diamondenhanced insert without sacrificing abrasive resistance at the cuttingface, and allows for the use of cutting elements having greaterextensions.

For example, another embodiment in accordance with aspects of thepresent invention is shown in FIG. 4. The bit 50 includes a bit body 52and a roller cone 54 rotatably coupled to the bit body 52. Cuttingelements 56, 57, 58 are disposed at selected locations on the cone 54and generally arranged in circumferential rows. At least one of thecutting elements 56 comprises an insert disposed in a socket formed inthe surface of the cone 54. In the example shown, the cutting element 56and a plurality of other similarly configured cutting elements aredisposed in the bottom contacting zone (36 in FIG. 2) of the bit 50. Theinsert (cutting element 56) includes an extending body 56A formed ofsteel and having a first end coupled to the cone 54 and a distal endextending in a direction away from the cone 54. A super hard element 56Bis embedded, including base and sides, in the distal end of theextending body 56A with an exposed surface to provide a wear resistantcutting tip. An enlarged partial cross-section view of cutting element56 on the cone 54 is shown in FIG. 5.

Referring to FIG. 5, the extending body 56A of the insert is disposed inthe socket formed in the surface of the cone 54. The extending body 56Amay be press fit, brazed, or attached to the cone 54 using a methodknown in the art. The other end of the extending body 56A (hereafterreferred to as the distal end) extends away from the surface of the cone54 an axial length (primary extension length), b. The insert furtherincludes a super hard element 56B that is press fit or otherwiseattached to a socket formed at the distal end of the extending body 56A.The super hard element 56B may be formed of any super hard material,such as polycrystalline diamond or polycrystalline cubic boron nitride.The super hard element 56B is configured such that when placed in thesocket of the extending body 56A it extends from the surface of theextending body 56A a distance (secondary extension length), t, to format least a portion of a cutting face for the cutting element. In theexample shown, the super hard element 56B forms the tip or crest of thecutting element 56 and is adapted to engage and cut through earthformations during drilling.

As illustrated in FIG. 5A, in accordance with another embodiment of thepresent invention, the super hard element may comprise a compact ofsuper hard material 59. The super hard compact 59 may comprise a body ofsuper hard material 59A bonded to a substrate 59B. In such case, thesubstrate 59B is disposed in the socket formed in the extending body(56A in FIGS. 4 and 5) of the cutting element (56 in FIGS. 4 and 5) andthe super hard material 59A is exposed proximal the distal end of theextending body (56A in FIG. 4) to form at least part of the cuttingface. The super hard element 59 in accordance with one example of anembodiment in accordance with the present invention may comprise apolycrystalline diamond body or layer bonded to a substrate formed oftungsten carbide infiltrated with a binder material.

Super hard elements 59 having substrates 59B may be brazed, press fit,or otherwise attached to the extending body of a cutting element inaccordance with embodiments of the present invention. Also, in variousembodiments of the invention, the super hard element may comprise anysuper hard material, such as polycrystalline diamond, cubic boronnitride, natural diamond, carbide or other super hard material. Thesuper hard element may further include a substrate formed from tungstencarbide, other metal carbide and/or other hard materials known in theart for making super hard compacts.

Referring back to the embodiment shown in FIG. 4, in addition to cuttingelements 56, the bit 50 also includes cutting elements 57 disposed onthe cone 54 which terminate into a substantially planar upper surface.In this example, cutting elements 57 are disposed in the wall contactingzone (35 in FIG. 2) and define the gage diameter of the bit 50. Thecutting elements 57 comprise tungsten carbide inserts disposed insockets formed on the cone 54. In other embodiments, these inserts maybe formed from tungsten carbide, other metal carbide, other hardmaterials, super hard materials, or combinations of hard and super hardmaterials known in the art, and may be formed as described in U.S.application Ser. No. 10/152,498 (“the '498 application”), titled “SingleCone Rock Bit Having Inserts Adapted to Maintain Hole Gage DuringDrilling,” which is incorporated by reference. In other embodiments,cutting elements 57 may be teeth formed on the cone and may includehardfacing.

The bit 50 also includes a plurality of cutting elements 58 disposed onthe cone 54 which terminate in a generally convex or rounded uppersurface. In this example, cutting elements 58 are tungsten carbideinserts press fit into sockets formed on the cone 54. Cutting elements58 are disposed on an inner row on the cone 54 between bottom contactingcutting elements and wall contacting cutting elements on the cone 54.Similar to cutting elements 57 above, in other embodiments cuttingelements 58 may be inserts or teeth formed on the cone and may includehardfacing.

Another embodiment in accordance with the present invention is shown inFIG. 6. In this embodiment, the single roller cone bit 60 includes asingle cone 62 rotatably mounted to the bit body 61 and having aplurality of cutting elements 63 mounted thereon. The cone 62 is amilled cone formed of steel. At least one of the cutting elements 63(cutting element 64) comprises a milled steel tooth 66 formed on thecone 62 and having a super hard element 68 partially embedded in thedistal end of the tooth 66. The super hard element 68 has an exposedsurface that extends from the end of tooth 66 to form a cutting face ortip for the tooth 66. In this embodiment, the tooth 66 has a box-likeform which tapers toward the distal end and has a substantial height (orextension) from the surface of the cone 62 to provide an aggressivecutting structure for the bit 60.

In some embodiments of the invention, the extension lengths of thecutting elements are selected to provide an aggressive cutting structurefor the bit and/or to allow for improve cutting structure or holecleaning. Benefits that may be obtained by providing cutting elementshaving substantial extensions from the cone surface are also disclosedin the '489 application. Referring to the example shown in FIG. 3, theprimary and secondary extension lengths, b and t, of the components ofcutting element 44 typically will be selected based on the bit size, thecutting element position on the cone, and the formation to be drilled.The total extension length L (L=b+t) of a cutting element in one or moreembodiments may be from 0 to 1 inches (about 0 to 25 mm) or more. In oneor more embodiments, the primary extension length b is at least about0.08 inches (about 2 mm), and a secondary extension length t is at leastabout 0.04 inches (about 1 mm) for drill bit diameters (27 in FIG. 2) ofbetween about 5 and 9 inches. For larger single roller cone drill bits,the primary and secondary extensions may be larger. For example, theprimary extension length b may be at least 0.30 inches (about 8 mm), andthe secondary extension length t may be at least about 0.06 inches(about 1.5 mm) when the drill bit has a drill bit diameter (27 in FIG.2) between about 9 to 18 inches.

For an example in accordance with FIG. 3, the extending body has aprimary extension length, b, of about 0.47 inches (about 12 mm) from thesurface of the cone, and the super hard element 46 has a secondaryextension, t, of about 0.09 inches (about 2 mm) from the surface of theextending body. This cutting structure was for a single cone bit havinga bit diameter of about 7.875 inches. In other embodiments, the cuttingelements may have a more substantial primary extension, such as 0.60inches (about 15 mm) or more depending on the type of formation beingdrilled.

In general, one or more cutting elements in accordance with one or moreembodiments of the invention may be disposed in a bottom contacting zone(36 in FIG. 2) of the cone. The cutting element may have a substantialprimary extension, such as at least 0.47 inches (about 12 mm) or more,to provide an aggressive bottomhole cutting structure for the bit. Suchcutting elements may also or alternatively be disposed in the wallcontacting zone (cutting elements 7, in FIG. 2) of the bit to maintaingage. The ratio of secondary extension to primary extension (t/b) for acutting element in accordance with the present invention may be selectedto have a value between 0 (flush mounted) and 1. In various embodimentsin accordance with aspects of the invention, the primary extension b ofthe extending body 45 will typically be between 0.08 to 1 inches (about2 to 25 mm), and the secondary extension t of the super hard element 46will typically be between 0 inches (flush mounted) and 0.4 inches (about10 mm).

The super hard material inserted in the steel extending body of thecutting element in accordance with one or more embodiments of theinvention may comprises any super hard material, including diamond,cubic boron nitride, or tungsten carbide. The super hard materialselected will typically depend on the particular formation expected tobe drilled by the bit. In one embodiment, the super hard element maycomprise a small polycrystalline diamond compact press fit into theextending body of the cutting element to form at least a portion of thecutting face for the cutting element. The polycrystalline diamondcompact may comprise a mass of polycrystalline diamond bonded tosubstrate formed of metal carbide or other material. In such case, thesubstrate may be press fit into the extending body of the cuttingelement and/or alternatively brazed to the cutting element.Additionally, for embodiments having polycrystalline diamond, thediamond body may also be partially or fully depleted of catalyzingmaterial for increased wear resistance. Also, in other embodiments,other materials may be disposed between the extending body and superhard insert to reduce interface stresses, improve impact resistance, orprovide better bonding between the super hard insert to the extendingbody.

Those skilled in the art will appreciate that cutting elementscomprising a hybrid insert including a steel body having super hardelement embedded therein, the cone may be formed from any material knownin the art, including steel or a matrix material, such as tungstencarbide infiltrated with a cobalt binder. For embodiments wherein thecone is formed of matrix material, the matrix material may beinfiltrated with natural diamond, thermally stable polycrystallinediamond (TSP), or other super hard material.

In one or more embodiments, a wear enhanced cutting element as describedabove may be used in conjunction with other types of cutting elements ona cone. For example, one or more cutting elements as described above maybe placed selectively placed in the high wear zones of the cone orintermittently placed in select regions of the cone. Also, in one ormore embodiments the cutting elements may be arranged differently thanthat shown. For example, in one embodiment, the cutting elements may berandomly arranged about the outer surface of the cone or arranged in aconfiguration other than rows. In one or more embodiments, the cuttingelements and/or the bit body may be coated with hardfacing material (notshown) to reduce wear on the cutting elements and/or the surface of thecone during drilling.

In one or more embodiments of the invention, because super hard materialis embedded in a softer more fracture resistant material and can belimited to the region near the cutting end of the cutting element 34, acutting element with a larger extension can be used to allow greaterpenetration in to the formation. Additionally hardfacing can be appliedover the extension material for increased wear resistance. Havingcutting elements with larger extensions compared to conventional diamondenhanced inserts available for single cone drill bits, also may allowfor better cuttings removal during drilling. Additionally, embodimentsof the invention allow for the use of larger inserts with longerextensions without the high cost and fragility associated withconventional diamond enhanced inserts.

A cutting element having a body formed from steel provides greatertoughness than a conventional diamond-enhanced insert. Bits formed inaccordance with one or more embodiments of the present invention maycomprise cutting structures which exhibit enhanced wear resistancewithout significantly sacrificing toughness.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A drill bit, comprising: a single rotatable cone; and at least onecutting element disposed on the cone, the at least one cutting elementcomprising: an extending body formed of steel and having a first endconnected to the cone and a distal end extending away from the cone, asuper hard element coupled to the distal end of the extending body andforming at least part of a cutting surface of the cutting element. 2.The bit of claim 1, wherein the extending body comprises a milled steeltooth formed on the cone.
 3. The bit of claim 1, wherein the extendingbody comprises an insert body disposed in a socket formed in the cone.4. The bit of claim 1, wherein the at least one cutting element isdisposed in a bottom contacting zone on the cone.
 5. The bit of claim 1,wherein the extending body has an extension length of at least about 12mm.
 6. The bit of claim 1, wherein the super hard element extends fromthe distal end of the extending body by at least about 2 mm.
 7. The bitof claim 1, wherein the super hard element comprises at least oneselected from the group of diamond, cubic boron nitride, and carbide. 8.The bit of claim 1, wherein the super hard element comprises a body ofsuper hard material bonded to a substrate.
 9. The bit of claim 1,wherein the super hard element is press fit in a socket formed in theextending body.
 10. The bit of claim 1, wherein the super hard elementis coupled to the extending body by brazing.
 11. The bit of claim 1,wherein the super hard element comprises a generally convex shapedsurface.
 12. The bit of claim 1, wherein the extended body is tapered atthe distal end.
 13. The bit of claim 1, further comprising a layer ofhardfacing disposed on at least a portion of the extending body.
 14. Thebit of claim 1, further comprising: a bit body adapted to be coupled toa drill string; and a bearing journal depending from the bit body,wherein the single roller cone is formed of steel and rotatably mountedon the bearing journal, the at least one cutting element is disposed onthe roller cone in a bottom contacting zone, and the extending body ofthe at least one cutting element comprises a milled steel tooth formedon the cone.
 15. The bit of claim 13, wherein the super hard element isdisposed in a socket formed at the distal end of the extending body, theextending body extends from the cone surface by at least about 10 mm,and the super hard element extends from the distal end of the extendingbody by at least about 2 mm.
 16. The bit of claim 1, further comprising:a bit body adapted to be coupled to a drill string; a bearing journaldepending from the bit body, wherein the single roller cone is formed ofsteel and rotatably mounted on the bearing journal, and the at least onecutting element is disposed in a bottom contacting zone on the cone, theat least one cutting element comprising an insert disposed in a socketformed on the cone.
 17. The bit of claim 16, wherein the super hardelement is disposed in a socket formed at the distal end of theextending body, the extending body extends from the cone surface by atleast about 10 mm and the super hard element extends from the distal endof the extending body by at least about 2 mm.
 18. A method for making adrill bit, comprising: rotationally coupling a single roller cone to ajournal depending from a drill bit body, providing at a selectedposition on the cone at least one cutting element having an extendingbody formed from steel and a super hard element coupled to a distal endof the extending body forming at least a part of an outer surface of thecutting element.
 19. The method of claim 18, further comprising coveringat least a portion of the outer surface of the extended body withhardfacing material.
 20. A drill bit, comprising: a single rotatablecone; and a plurality of cutting elements disposed on the cone, theplurality of cutting elements comprising a first set of cutting elementsdisposed in a first region of the cone and a second set of cuttingelements disposed in a second region of the cone, wherein at least oneof the cutting elements in the first region comprises: an extending bodyformed of steel and having a first end connected to the cone and adistal end extending away from the cone, a super hard element coupled tothe distal end of the extending body and forming at least part of acutting surface of the cutting element.